Instructions

1. Line 12 muffin cups (link to my favs below)
2. Whisk egg in medium bowl.
3. Add yogurt, sour cream, oil, sugar, and vanilla and whisk until thoroughly combined.
4. Add in flour, cocoa, baking powder, baking soda, and salt and stir just until combined.
5. Preheat oven to 375° and let batter sit while oven is preheating. This eliminates any gritty texture.
6. Divide batter between muffin cups. The muffin cups will appear very full, but that's ok. They will puff up but the batter is thick enough they won't run over the edge and overflow.
7. Sprinkle generously with crumb topping. 
8. Bake about 13-15 minutes, until toothpick inserted in center muffin comes out clean. Watch carefully and remove as soon as they are done so they don't dry out.